NKT was established in 1891 as cable manufacturer. In 1999 NKT A/S Denmark merged with Felten & Guilleaume Kabelwerke GmbH in Germany to form nkt cables group GmbH with headquarters in Cologne. nkt cables group GmbH is owned by NKT Holding A/S, an industrial group of companies employing 5.000 people. nkt cables group GmbH bundles the expertise of around 2.500 employees in 10 production and development facilities spread over four European countries and P.R. China. Manufacturing and developing power cable accessories up to 42 kV is one of the core businesses of nkt cables group GmbH. Since more than 50 years nkt cables GmbH Nordenham, Germany (formerly F&G Kabelgarnituren GmbH) is one of the world market leaders in power cable accessories. The product range covers cable joints, cable connectors for SF6switchgears and transformers as well as indoor- and outdoor terminations. These types of cable accessories are used for single- and 3-core cables as well as for paper insulated cables. As the ﬁrst company introducing silicone rubber terminations already in the sixties, nkt cables GmbH, Nordenham is specialized in production of silicone rubber power cable accessories.

The speciﬁc electrical problems of the cable termination are found at the point between the high-grade solid electrical insulation of the cable and the gaseous insulation air which has a signiﬁcantly lower dielectric strength. In order to achieve sufﬁcient insulating clearance, the outer conductive layer of the cable must be stripped to below the end of the core. This causes unacceptably high ﬁeld intensities at the end of the outer conductive layer (ﬁgure 1) which must be eliminated by means of special measures. Figure 2 shows the ﬁeld of the cable termination controlled capacitively by a funnel shaped electrode. It is dimensioned in such a way that ﬁeld intensities do not exceed at any point. This prevents harmful corona or partial discharge.

Figure 1 Electrical field without stress control

Conductor Core isulation

Figure 2 Electrical field with capacitive stress control

Conductor Core isulation

Equipotential lines Equipotential lines

Field lines Field lines

Stress cone

Outer conductive layer Screening wires Outer sheath

Outer conductive layer Screening wires

Outer sheath

4

Silicone rubber

Silicone rubber is a preferred material for cable accessories due to its excellent mechanical and electrical properties. For more than 40 years silicone has been used successfully as highquality electrical insulation for voltages up to 400 kV. Silicone rubber features high quality electrical insulation, superior corona and tracking resistance, combined with high elasticity. It facilitates multi range application, where one silicone rubber body can be used for various conductor cross sections. Optimal ﬂexibility ensures easy assembly of the accessories. Outstanding features of the silicone rubber insulation material are: ● UV and ozone resistance ● durable water rejection ● weather and aging resistance ● non-ﬂammable, self-extinguishing, heat resistant ● applicable for use at temperatures between -50° C and +180° C ● high elasticity ● high tracking resistance ● unlimited storage life ● friendly to the enviroment